In an effort to improve fuel economy, internal combustion engines incorporate camshaft scheduling strategies, which regulate camshaft timing based primarily on engine speed (RPM) and engine load, where the engine load is determined based on airflow, e.g. trapped air per cylinder (APC), relative load (displacement scaled APC) or other measure of volumetric efficiency.
One known technique of controlling engine load is Late Intake Valve Closing (LIVC). In LIVC, intake throttling is replaced with intake back-flow, i.e. gases are returned back to the intake manifold until the required charge is obtained inside the cylinder, effectively reducing pumping losses within the system.
However, because known camshaft scheduling strategies utilize APC based tables and further because LIVC, in the high-mid load region of the engine operating range, causes a disproportionately large change in manifold absolute pressure (MAP) with respect to a relatively small change in APC, these known camshaft scheduling strategies limit the application of LIVC to the low load region of the engine operating range.
Therefore, while these known camshaft scheduling strategies are useful to improve fuel economy, such improvement is limited to the low load region of the engine operating range and results in sub-optimal fuel efficiency in the high-mid load operating range.